Problem: What is Kf for water if the freezing point was lowered to -12°C once 30 g of Sodium Chloride was added to 150 g of water?

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We’re being asked to find the Kf (freezing point depression constant) of water if its freezing point decreased to -12°C when NaCl was dissolved in it. We’re going to use the Freezing Point Depression equation to calculate for Kf.


∆Tf = change in freezing point = Tf pure solvent –Tf solution
Kf = freezing point depression constant
i = van' t Hoff factor of the solute = no. of ions
m = molality


Let’s first calculate the molality of the solution. 

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What is Kf for water if the freezing point was lowered to -12°C once 30 g of Sodium Chloride was added to 150 g of water?

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Our tutors have indicated that to solve this problem you will need to apply the Freezing Point Depression concept. If you need more Freezing Point Depression practice, you can also practice Freezing Point Depression practice problems.

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Based on our data, we think this problem is relevant for Professor Chakraborty's class at FIU.